you can either buy pre-cut fenders that have the perfect slot already, or you can cut them. rust can be a result, but as long as you coat the bear metal with some kind of paint or even bondo (remember it will be under the light) it shouldnt rust. as for water leakage, i think that the ctr sidemarker kit includes a grommet, even though it probably wouldnt be hard to make one of you own. oh yeah, if you haven't gotten them yet, check ebay for cheap ass prices.